1. Field of the Invention
This invention relates to medical devices and procedures. In particular, this invention relates to devices and methods for reducing the forces encountered during delivery and deployment of medical devices, to alleviate or reduce physician fatigue.
2. Description of Related Art
Endoluminal prostheses, such as stents and stent grafts, are used for treating damaged or diseased body lumens such as the esophagus, bile duct, and blood vessels. For example, endoluminal prostheses may be used for repairing the diseased aorta including abdominal aortic aneurysms, thoracic aortic aneurysms, and other such aneurysms. The prosthesis is placed inside the body lumen and provides some or all of the functionality of the original, healthy vessel.
The deployment of endoluminal prostheses into the lumen of a patient from a remote location by the use of a catheter delivery and deployment device is well known in the art. For example, PCT Publication No. WO 98/53761 entitled “A Prosthesis and a Method and Means of Deploying a Prosthesis,” which is incorporated herein by reference, proposes a delivery and deployment system for an endoluminal prosthesis. The prosthesis is radially compressed onto a delivery catheter and is covered by an outer sheath. To deploy the system, the operator slides the outer sheath over the delivery catheter, thereby exposing the prosthesis. The prosthesis expands outwardly upon removal of the sheath. Such a delivery and deployment device has been referred to as a “push-pull” system because as the operator pulls the sheath proximally in relation to the delivery catheter, the delivery catheter pushes the prosthesis out of the sheath.
Devices, such as the ones described in WO 98/53761 have several advantages. To deploy the prosthesis, the operator can directly manipulate the sheath and the delivery catheter. This provides the operator with a relatively high degree of control during the procedure. Further, such devices may be compact and may have a relatively uniform, low-diameter radial profile, allowing for atraumatic access and delivery.
With some catheter delivery and deployment devices, the force required to withdraw the sheath may be relatively high. The withdrawal force is a function of various factors including, for example, frictional resistance caused by the sliding engagement between components of the system such as the sheath, the delivery catheter, the prosthesis, and the hemostatic valve assembly. A delivery and deployment device may require as much as 100 Newtons or approximately 22.5 pounds of force to deploy. This force is transferred to the physician performing the procedure. Such force can easily tire an operator and, accordingly, is highly undesirable.
Motors, springs, gears, and other such devices, have been proposed to reduce the force required to withdraw the sheath over the delivery catheter. Examples of such devices are described in U.S. application Ser. No. 11/764,969, entitled “Prosthesis Delivery and Deployment Device,” and U.S. App. Ser. No. 60/950,001, entitled “Prosthesis Delivery and Deployment Device,” each of which are herein incorporated by reference. Additionally, various lubricants and lubrication methods have been proposed to reduce the force required to insert a catheter into a sheath. For example, in some methods a lubricant, such as a medical-grade silicone, is applied to the catheter before the catheter is inserted into the sheath. The lubricated catheter is then inserted into the sheath through a hemostatic valve. The force required to place the catheter is reduced by virtue of the presence of the lubricant on the catheter.
Once the delivery catheter is placed within the sheath lumen, the delivery and deployment device may be stored for days, weeks, or even months, before the device is used. During this time, the valve presses against the delivery catheter and forms a static bond. The force required to overcome this static bond often constitutes a significant portion of the entire sheath withdrawal force. The lubrication methods described above rely on the sliding interaction between the catheter and the valve and, therefore, are advantageous for reducing dynamic or sliding friction. However, these methods are generally ineffective for reducing static friction. Thus, there is a need for alternative devices and methods for decreasing the sheath withdrawal resistance of a delivery and deployment device, resulting from both dynamic and static friction.